When a surgeon operates endoscopically in gas filled body spaces, he needs trocar sleeves with a gas seal to introduce the instruments in order to prevent the gas from escaping. The most common field of application is laparoscopy, that is to say working in the stomach space expanded with pressurized gas. One or more gas sealed trocar sleeves are positioned through the stomach wall and provide the necessary access for various instruments, such as optical systems, forceps, cutters and the like which are constructed with the necessary length.
A wide variety of constructions are known for sealing the trocar sleeves to prevent the escape of gas. The known seals are generally constructed in the form of non-return flap valves which are opened by the instrument when it is introduced and automatically close when the instrument is withdrawn. The Duckbill valves are constructionally particularly simple and these close the slit with their oblique walls under a pressure load from the insertion tube, which slit, however, when an instrument is inserted, is easily opened from the exterior. In addition to this non-retum flap valve, elastic apertured diaphragms are generally also provided on the external openings of the valve chambers. Such diaphragms elastically surround the shaft of the instrument and are responsible for the seal when the instrument is inserted and the valve is thus open. The prior art shows such constructions of the type referred to above, e.g. in EP0652730 B1 and U.S. Pat. No. 5,141,498, with a special construction with transverse slits. However, duckbill valves have the disadvantage, like most flap valves, that they do not close cleanly when there is a very low pressure in the body space. Thus if for example the stomach space is gradually pressurised by the injection of gas, gas can still escape through the duckbill valve which can prevent the build up of pressure in the stomach space.
It is the object of the present invention to provide a trocar sleeve of the type referred to above which closes cleanly even at a low pressure differential.
If the duckbill valve is oversized in the direction transverse to the slit with respect to the internal size of the valve chamber, in the uninstalled rest state, it will be compressed transverse to the slit when instaled in the valve chamber. The elastic material of the duckbill valve then exerts a closing biasing force on the slit which holds the valve closed, even at a very low pressure differential. The valve will stay closed without the pressure forces on the oblique surfaces acting to close the slit. A trocar sleeve in accordance with the invention, can thus form a seal, during a pressure build up, even to the lowest pressures, so that the pressure build up in the body space can proceed undisturbed.
The oversize of the tubular body transverse to the slit can be produced by the tubular body having the correct size in this direction but the valve chamber being undersized. This has the advantage that a duckbill valve of standard construction may be used. On the other hand, the valve can be provided oversized and the valve chamber in the correct size, which offers the advantage of, for instance, being able to retrofit it to existing standard trocar sleeves.
Accordingly, the term xe2x80x9coversizedxe2x80x9d as used herein is meant to indicate the condition wherein the tubular body is larger, in a width dimension, that the corresponding portion of the valve chamber such that the tubular body must be compressed to be inserted into the valve chamber. In one instance, the tubular body is circular and is to be inserted into an oval valve chamber. When at rest or uninstalled, the tubular body has a diameter that is larger than the short side of the oval valve chamber. Accordingly, the tubular body must be compressed to fit within the short side of the valve chamber, and compression of the tubular body takes place in a direction essentially transverse to the slit. Alternatively, the tubular body, at rest, is oval-shaped and the valve chamber is circular. In this case, the slit in the tubular body traverses the short side of the oval tubular body. Since the long side of the tubular body is longer than the circular valve chamber, in order to fit within the valve chamber, the long side of the tubular body must be compressed. In either case, the tubular body has an at-rest or uninstalled size dimension, in a direction transverse to the length of the slit, of a first value and the valve chamber has a size dimension of a second value. The first value is larger than the second value such that, during installation, compression of the tubular body takes place essentially transverse to the length of the slit.
Since valve chambers commonly have circular internal cross-sectional shapes, it is recommended that the oversize be created by a slight oval deviation from the circular standard cross-sectional shape but attention should be paid to the correct angular positioning of the oval shape with respect to the direction of the slit in order to produce the desired compression of the duckbill valve transverse to the slit.
In further accordance with the present invention a standard trocar sleeve with a circular internal cross-sectional shape of the valve chamber can be used. The exact positioning of the oversize transverse to the slit is produced during manufacture of the duckbill valve. When inserting the duckbill valve into the- valve chamber no attention need be paid to the angular position so that installation is simplified.